Units in CamDRAW: Document Unit vs Application Setting

Units in CamDRAW confuse people because there are two of them, and they do different things. Understanding which one governs your job takes about a minute and prevents the most avoidable class of mistake on a CNC machine.

The rule

CamDRAW always works with the current CorelDRAW document unit, even when the unit stored in its own settings is different.

That is the whole rule. Everything else follows from it.

What the setting in the preferences does

Click the gear icon at the very top of the CamDRAW docker, next to the logo. On the General tab there is a dropdown labelled Unit (Create new document), offering MM or INCH.

This governs one thing only: the unit used when CamDRAW creates a new CorelDRAW document for you, which happens when you enter workpiece dimensions with no document open. It is a default for new documents, not a global setting.

Click Save at the bottom of the window to keep a change.

Changing the unit of the document you are working in

This is done in CorelDRAW, not in CamDRAW.

With no object selected, look at the property bar along the top of the CorelDRAW window. There is a dropdown labelled Units. Change it there and the whole document switches.

All CorelDRAW length units are supported, not only millimetres and inches. Centimetres, metres, points and the rest all work, because CamDRAW reads whatever the document is set to.

What the document unit affects

Once set, the document unit governes several things at once:

• The unit abbreviations shown behind the input fields in CamDRAW

• The values you type into operations: safety height, depth, engraving height, curve precision

• The G-code that is generated, including whether the program is written in inches or millimetres

• Which tool list is used

That last point catches people out, so it gets its own section.

Two tool lists, chosen automatically

CamDRAW installs two tool libraries: one holding tools with parameters in inches, one in millimetres. Both live in your settings folder as Tools_INCH.tdb and Tools_MM.tdb.

When you open the tool list, CamDRAW opens the one matching the current document unit. A millimetre document opens the millimetre list, an inch document the inch list, and any other unit opens the inch list.

So if you set up your tools carefully and then find the library apparently empty of them, check the document unit first. You are almost certainly looking at the other list.

The sensible working habit

Use one unit throughout: document unit, machine unit and tool unit the same. Mixing them is technically possible and rarely worth the risk.

Set the unit before you start rather than partway through. Changing it midway is allowed, but values you already entered were interpreted in the old unit, and the numbers in existing operations do not convert themselves.

Checking before you cut

After generating a program, open it with the text editor icon in the NC program section of the docker and look at the first lines. The preset writes either G20 for inches or G21 for millimetres, depending on the document unit. Thirty seconds there is cheaper than a part cut at 25.4 times the intended size.